Implement Clone to support old compilers

Arrays above size 32 are not Clone on old compilers.

src/lib.rs

@@ -49,7 +49,7 @@ pub fn fmt<W: fmt::Write, V: Integer>(mut wr: W, value: V) -> fmt::Result {
 /// let printed = buffer.format(1234);
 /// assert_eq!(printed, "1234");
 /// ```
-#[derive(Copy, Clone)]
+#[derive(Copy)]
 pub struct Buffer {
     bytes: [u8; I128_MAX_LEN],
 }
@@ -61,6 +61,13 @@ impl Default for Buffer {
     }
 }
 
+impl Clone for Buffer {
+    #[inline]
+    fn clone(&self) -> Self {
+        Buffer::new()
+    }
+}
+
 impl Buffer {
     /// This is a cheap operation; you don't need to worry about reusing buffers
     /// for efficiency.